This project is a competitive renewal of a grant that we have had since 2001. Work supported by this grant has demonstrated that stress can act via a variety of mechanisms to elevate the function of the transcription factor cAMP response element binding protein (CREB) in the nucleus accumbens (NAc). Elevated CREB function in the NAc produces depressive- and anxiety-like effects that are due, at least in part, to CREB-regulated increases in expression of dynorphin (DYN), an opioid peptide that acts at kappa-opioid receptors (KORs). Identifying this mechanism led directly to findings that KOR antagonists have antidepressant-like and anxiolytic-like effects in preclinical screening assays that identify standard medications from these drug classes. This combined antidepressant/anxiolytic profile is unique and not shared by any existing medications, and has piqued interest in the development of these drugs for depressive disorders. As KOR antagonists move toward clinical studies, important questions about their mechanisms of action have emerged. In addition, superimposed on growing enthusiasm for KORs as a therapeutic target is increasing skepticism regarding the usefulness of preclinical (laboratory animal-based) screening assays in drug development. Current experiments will broaden our understanding of how CREB and KOR function affect behavior while focusing on domains (hypervigilance, sleep, and decision-making) in rodents that are objective, cut across numerous types of psychiatric illness, and can be studied in humans using endpoints that are virtually (or precisely) identical. We will characterize the neural circuits that regulate these domains and the mechanisms by which the regulation occurs, which may facilitate validation of endpoints that have better predictive value for clinical studies. Our research utilizes cutting-edge molecular tools, engineered mice, pharmacology, and behavioral assays in male and female rodents to accomplish numerous goals. In Aim 1, we will continue to characterize the circuits in which KORs are critical for stress responses, and explore the possibility that KOR antagonists have off-target (non KOR-related) actions that contribute to their putative therapeutic effects. In Aim 2, we will examine the roles of CREB and KORs in stress effects on sleep and circadian rhythms, disruptions in which are a core feature of myriad psychiatric disorders. In Aim 3, we will examine how stress affects interactions between DYN and orexin (ORX), following up on our discovery that these peptides act in tandem despite opposing effects on neural function and behavior. In Aim 4, we will characterize the roles of KORs and ORX receptors (ORXRs) in a complex cognitive impairment (post-error decision-making) that is a core feature of depressive illness and readily apparent in laboratory animals (rats) given treatments that cause depressive-like behaviors. Collectively, this work is designed to hasten the development of improved treatments for psychiatric illness while at the same time being responsive NIMH priorities with respect to (1) studying behavioral dimensions that cut across numerous disorders and (2) considering sex differences as a biological variable.